Crabs - Swimming Crabs (Family Portunidae) can be characterized by the lateral spine on each side of the body, elongated eyestalks, and a flattened leaf-shaped paddle on the last pair of legs. Many species in this family are excellent swimmers. Included in this family is the Blue Crab (Callinectes sapidus) which is of great commercial value as a table food. As many as eighty million pounds of Blue Crabs have been "harvested" in a year.

Crabs (DecapodaBrachyura) are a group of the Shrimp and Crab Order (Order Decapoda). The crabs are a diverse group. However, one can usually recognize a crab because of its small abdomen, and a thorax that may be as wide as or wider than it is long.

Shrimps and Crabs (Order Decapoda) contains most of the larger freshwater and marine species of crabs, crayfish, shrimp, and lobsters. They have a total of ten pairs of legs, four pairs of which are used for walking. Frequently the first pair of legs has been modified into pinchers used for eating and defense.

Here the Decapoda have been separated into five different suborders that match the adult shapes of the various life forms. They are as follows:

Natantia - Shrimp-like
Brachyura - Crab-like
Anomura - Hermit Crabs and relatives
Astacidea - Crayfish and Lobster-like
Palinura - Spiney Lobsters and Spanish Lobster

The sub-classification of the Order Decapoda is in a state of change. For a short summary of this situation, please refer to pages two and three of "Shrimps, Lobsters, and Crabs of the Atlantic Coast of the Eastern United States" by Austin Williams published by the Smithsonian Press, Washington, D.C., in l984. If one uses adult shape for classification, one gets one organization, and if one uses larvae shape for classification, one gets a different organization.

Crustaceans (Class Crustacea) is a large class of mostly aquatic animals. Although many species are marine, there is a large number of small freshwater species and a few species of larger freshwater crayfish. There are many subdivisions to the Crustacea including such diverse animals as water fleas, fish lice, barnacles, crabs, shrimp, and crayfish. There are probably over 26,000 species in this class.

Jointed Legged Animals (Phylum Arthropoda) make up the largest phylum. There are probably more than one million different species of arthropods known to science. It is also the most successful animal phylum in terms of the total number of living organisms.

Butterflies, beetles, grasshoppers, various insects, spiders, and crabs are well-known arthropods.

The phylum is usually broken into the following five main classes:
Arachnida: - Spiders and Scorpions
Crustacea: - Crabs and Crayfish
Chilopoda: - Centipedes
Diplopoda: - Millipedes
Insecta: - Insects

There are several other "rare" classes in the arthropods that should be mentioned. A more formal list is as follows:

Sub Phylum Chelicerata
C. Arachnida: - Spiders and scorpions
C. Pycnogonida: - Sea spiders (500 species)
C. Merostomata: - Mostly fossil species

Sub Phylum Mandibulata
C. Crustacea: - Crabs and crayfish

Myriapod Group
C. Chilopoda: - Centipedes
C. Diplopoda: - Millipedes
C. Pauropoda: - Tiny millipede-like
C. Symphyla: - Garden centipedes

Insect Group
C. Insecta: - Insects

The above list does not include some extinct classes of Arthropods such as the Trilobites.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.

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